Method of making stencil sheets and resultant article



United States Patent IVIETHOD OF MAKING STENCIL SHEETS AND RESULTANT ARTICLE Keith S. Hoover,'Elmhurst, and Bror E. Anderson, Park Ridge, 111., assignors to A. B. Dick Company, Niles, 11]., a corporation of Illinois No Drawing. Application November 1, 1950, Serial No. 193,527

8 Claims. (Cl. 117-355) This invention relates to stencil sheets and particularly to a stencil sheet adapted for use with stencil duplicating like, with a yieldable composition that is displaceable when acted upon by a typewriter, stylus or the like to form openings or passages through which ink may be transmitted. In stencil duplication, ink is transmitted through the passages in the base tissue to reproduce on paper or the like the characters formed in the stencil sheet. The coating composition is usually a film-forming material such as a protein, a cellulose ester or cellulose ether derivative or a synthetic resinor the like, usually modified by one or more plasticizers to produce a coating having the desired yield characteristics.

The qualities most desired in a stencil sheet include ease of stencilization, cleanliness of stencilization (that is, freedom of particles of coating composition clinging to the exposed fibers), resistance of the fibers to cutting by the typewriter key or stylus, resistance of the base tissue and of the coating composition to softening or other reaction with the ink employed, and it is desired to have tissue of high strength and capable of being filed away without excessive harm or deterioration.

Stencil sheets of the type heretofore produced have possessed these qualities in some degree and in many instances have performed satisfactorily in stencil duplication. This is true especially when used in combination with standard oil-base inks having little, if any, aqueous content. In such inks, oil is usually present in amounts ringing up to 90 percent by weight as the continuous p ase.

The same, however, is not true with respect to their use with the more recently developed water-base stencil duplicating inks. With the advent of rapidly drying stencil inks of the water-base and water emulsion types, the situation has changed radically. It has been found that stencil sheets satisfactory for use with oil-base inks are unable to give long life and good copy quality when used with inks having a high proportion of aqueous medium. With the use of water-base inks in combination with stencil sheets of the type heretofore produced, runs are shorter and the copy has an inferior appearance, particularly with respect to distortion, such as stretch and sag which take place usually after a number of copies have been made. stencil sheets seem to disintegrate and fall apart in several places and become so weak as to be unusable. The lack of a suitable stencil sheet has retarded the advancement and the widespread use of the more desirable water-base and emulsion type inks and has prevented the enjoyment of their outstanding advantages, such as extremely rapid drying and freedom from set-off.

It is an object of this invention to produce a stencil sheet possessing greatly improved durability, especially when used with ink compositions having substantial water content, such as the water-base and water emulsion inks.

Another object is to produce a stencil sheet which has greater inherent durability under conditions of use and it is a related object to produce a; stencil sheet which The Before long the 2,693,426 Patented Nov. 2, 1954 has the desired operating characteristics when used with water-base and water emulsion inks.

A further ob ect is to produce a new and improved coating composition for use in the manufacture or stencn sheets.

A still further object is to produce a stencil sheet having the characteristics of improved ease or stencinzatlOn.

in accordance with this invention a stencil sheet having greatly improved characteristics which adapts it particularly for use with water-base and emulsion type inks maybe produced by providing a base tissue possessing (a) an exceptionally low "tensile ratio, (1)) a high basis weight, (c) substantial wet strength, and (d) coating the base tissue with a composition formulated with a plasticizer constituted of an alkylated phenol, which will hereinafter be described.

By the term tensile ratio of the base tissue, as used in the specification and claims, we mean the ratio of the tensile strength, dry, in the cross direction, to the tensile strength, dry, in the machine direction, the tensile strength in both cases being determined on a two inch width and expressed in grams. By cross direction we mean in a direction perpendicular to the direction of travel of the tissue web when on the paper machine, and by machine direction we mean in a direction parallel to the travel of the web. The tissue is cut and the stencil sheets are mounted in such manner that the machine direction of the tissue is in the long direction of the stencil. A sheet that has equal strength in both directions would have a tensile ratio of percent. By wet strength we mean the tensile strength, expressed in grams, of a two inch width of the tissue after thorough wetting with water.

The tensile ratio of the base tissue used in the conventional sheets of the prior art is typically about 50 to 80 percent. This is true regardless of whether abaca, Kozo, or other fiber is employed in the tissue.

An important concept of this invention resides in the discovery that when the tensile strength of the dry sheet measured in the machine direction is kept Within certain limiting values, the durability of the sheet may be increased about two to five fold or more by regulating the distribution of fibers to provide a tensile strength in the cross direction having only 10 to 40 percent of the tensile strength in the machine direction. This amounts vto the manufacture of a stencil sheet employing a tensile ratio of only 10 to 40 percent and preferably about 15 to 20 percent. It has been found that the limiting values of the tensile strength of the dry sheet measured in the machine direction are from about 2500 to 5500 grams per 2 inch width, with a preferred range of about 3000 to 4000 grams.

With other conditions being held the same, the ratio of tensile strengths in the cross and machine directions is found to depend somewhat on the degree of orientation of fibers in those directions. It has been found that either obtaining greater orientation of fibers in the machine direction or obtaining a greater proportion of the total possible stretching of the web in the machine I direction is a desirable step for producing a stencil base tissue of improved durability characteristics. With conventional paper machine driers in which paper is dried by contact with heated metal surfaces, the paper may be stretched slightly, or at least prevented from shrinking, by the tension of the web in the machine direction.

In practice, when the orientation of the fibers in the machine direction is increased, the inherent stretchability in the machine direction is decreased. If a highly oriented tissue is made with no relative speed changes on the machine, it becomes stretched a greater proportion of its total possible stretch in the machine direction, as compared with a less oriented tissue.

Low tensile ratio tissues can be produced either by increasing the orientation of the component fibers in the machine direction while producing the sheet, or by a proportionately greater stretching of the sheet in the machine direction or, preferably, by both techniques. The optimum tensile ratios which may be secured in accordance with this invention are to be regarded as the results of controlled fiber orientation in certain directions to the extent required to produce specified ratios.

For maximum number of good quality copies with water-base and emulsion type duplicating inks, it has been found desirable, and .in many. .instances necessary, to employ a base tissueuof. appreciably higher .weight basis than has heretoforebeen-used in the art. .Specifically, .when referring to weight basis interms of pounds per 480 sheets (24" x 36") it has been founddesirable to employ tissue having a basis weight of. about 6.5.to 8.5 pounds as compared with 5.9 to 6.2, pounds heretofore employed. It is preferred to run at sufficiently higher average vbasis weight inorder to minimize the possibility of thepresence of ,tissuehaving a basis .weight below 6.5 pounds.

It has also been found that good wet strength, contributes materially to the performance .of the tissue, particularly whenthe tissue is.of high basis weightand low tensile ratio. The lower limit .is in. the order of 200 grams and may vrangeto as high as about 500 grams, with about 300 grams being best for the wet tensile strength in the .machine direction. The ,desired Wet strength may besecured by Well known means, such for example as by treatment with a water soluble resin capable of being reacted to effect at least a partial insolubilization thereof in the base tissue. Resinousimaterials having characteristics .of the type described may be selected of urea formaldehyde resin, melamine-formaldehyde resin, polyvinyl alcohol, methyl cellulose, hydroxyethylcellulose and other cellulose derivatives capable of insolubilization, by acetal reaction. While it has been discovered that great improvement in durability results from low tensile ratio alone, it has also been found that when this factor is combined with wet strength or higher basis weight, ,the effect on durability is synergistic. This is particularly true when all of these factors are combined.

The improved base tissuemay be treated with conventional coating compositions to produce finished stencil sheets capable of making a greater number of copies. The improvement is most apparent in the use of the stencil base tissue with water-base or emulsion type inks. This greatly increased durability is sometimes accompanied by an undesirable reduction in the ease of stencilization. This is objectionable because it prevents attainmentof good copy quality.

It has been found that this deficiency may be overcome by formulation witha novel type of plasticizer in coating composition. This preferred plasticizer is described in United States Patent No. 2,502,003, which issued on March 28, 1950. Briefly described, the plasticizer is selected from the general class of alkylated phenols and more specifically, aralkyl-phenolic condensation product prepared by the reaction of an aromatic vinyl compound and a not less than about an equal molecular proportion of phenol in an inert solvent, and in the presence of a catalyst which promotescondensation and polymerization. Aromatic vinyl compunds which may be used are of the type styrene and its derivatives. The term phenols is understood to include phenol, cresols, xylenols, naphthols and various substituted phenols, such as are set forth in the patent referred to above. The particular type of plasticizer may be diluted with alcohol to form a viscous reddish-brown liquid and is sold commercially with a specific gravity of about 1.08 at 30 C. It has a molecular weight of about 250, and boils above 300 C. at atmospheric conditions. The average refractive index is about 1.599 at 25 C.

While this plasticizer is soluble in alcohol and com patible with the cellulose derivatives and proteins often employed as the film-formers in stencil coatings compositions, a very successful result has been secured in the use of this plasticizer with nitro cellulose which is most often used as a film former for stencil sheets. When iiitro cellulose coating compositions are formulated With about 20 percent by weight of this type of plasticizer, the ease of stencilization and copy quality are much better than obtained with other plasticizers. It is desirable to employ the plasticizer in amounts ranging from about 15 to 20 percent of coating composition but larger amounts may be used. More than 30 percent, however, tends to make the coating too soft and too easily stencilized so that an excess of ink is permitted to flow through the openings, producing uneven copy and impairing the life ,of the stencil. Less than 15 percent may be used but little improvement is secured if the amount falls below 10 percent.

The following two examples are typical of coating compositions employing the new plasticizer which we have used successfully:

Example 1 Material: Percentage Nitrocellulose Pollygtliylene glycoldi-Z-ethyl hexoate (Flexol Stearic acid Halowax Mineral oil Benzyl alcohol Sorbitol mono oleate (Span 80) Oleic acid Green Toner Tannic acid H.

Nevillac TS (aromaticv vinyl-phenol condensation product) Total 100.0

Example 2 Color, apigment (Green Toner) in Example 1, ora dye (Victor a.,Blue).;in Example 2, is usually incorporated in stencil coat ng compositions so that displacement of ,a coating by a typewriter key or stylus provides suificient contrast to permit full determination of the stencilled characters. .Instead of -Grecn Toner or Victoria Blu other pigments and dyes may be used, such for example as tungstated or molybdated brilliant green dye, including tungstated N-tetraethyl triphenylmethane or malachite green which is-tungstated N-tetramethyl v,triphenylmethane or pigment such asqsoda or potash blue, Hansa yellow, lithopone, titanium dioxide and ;the like.

Although coating compositions formulated with a substantial amount of the alkylated phenol plasticizer have particular. value .when applied ;to stencilv sheets haying'a low tensile ratio,,highbasisweight and wet strength, particularly when used with water-base and emulsion type inks, such coating compositions .may also beapplied, to advantage onto conventional base tissues to form stencil sheets characterized. by increasedease of stencilization and improved copy .quality. It will be apparentthat we have produced a newand improved stencil sheet showing marked. superiority when used with .water-baseand emulsion type inks. .Although greatest unprovernentis experienced .whenused with .inks containing watenfthe stencil sheet embodying features of this. invention is ,used .to advantage ,with other type ink compositions, such as oil-base inks, spirit inks andthe like. Theimprovementresultsfrom the unique cooperative relationship of animproved pressure-sensitive stencil coating compositionanda particular typeof base tissue, each of whichhave separate and. individual utility in the stencilart.

It will be understood that particular utilization of ,the basic principles of this invention are susceptible to a great number of modifications with respect to materials, percentages and methods of application.

It will be further understood that numerous changes may be made Without departing'from 'the,, spirit of the invention, especiallyasdefined by the following claims.

We claim: 4

l. -A process for preparingstencil sheets which comprises depositinga coating composition containingcellulose-nitrate as. the principal film former and 15 to 25 percent-ofapolymerizable reaction product o f an aromatic vinyl compound with not less than an equimolecular equivalent of phenol as a plasticizer on a porous base tissue in which the dry tensile strength in the longitudinal direction is between 2500-5500 grams for a two inch width while the dry tensile strength in the transverse direction is from -40 percent of said longitudinal tensile strength, a minimum wet strength in the machine direction of about 200 grams, both wet and dry tensile strengths being for a two inch width, and a basis weight of about 6.5 to about 8.5 pounds for 480 sheets 24 by 36 inches in dimension.

2. A stencil sheet comprising a porous base tissue formed of fibers highly oriented in the machine direction in which the dry tensile strength in the longitudinal direction is a minimum of 2500 grams for a two inch width'while the dry tensile strength in the transverse direction is from 10-40 percent of said longitudinal tensile strength, and a stencilizable coating on the base tissue.

3. A stencil sheet comprising a porous base tissue formed of fibers highly oriented in the machine direction in which the dry tensile strength in the longitudinal direction is a minimum of 2500 grams for a two inch width while the dry tensile strength in the transverse direction is from 10-40 percent of said longitudinal tensile strength, a basis weight of 6.5 to 8.5 pounds calculated as the weight of 480 sheets of 24 by 36 inches, and a stencilizable coating on the base tissue.

4. A stencil sheet comprising a porous base tissue formed of fibers highly oriented in the machine direction in which the dry tensile strength in the longitudinal direction is between 2500-5000 grams for a two inch width while the dry tensile strength in the transverse direction is from 10-40 percent of said longitudinal.

tensile strength, a basis weight of 6.5 to 8.5 pounds calculated as the weight of 480 sheets of 24 by 36 inches, a wet strength of at least 200 grams per two inch width in the machine direction, and a stencilizable coating on the base tissue.

5. A stencil sheet comprising a thin porous base tissue and a stencilizable coating on the tissue formulated with nitrocellulose and containing -25 percent by weight plasticizer in the form of the polymerization reaction product of an aromatic vinyl compound with not less thanabout an equal molecular proportion of phenol.

6. A stencil sheet comprising a thin porous base tissue formed of fibers highly oriented in the machine direction and characterized by a tensile ratio of 10-40 percent, and a stencilizable coating on the base tissue formulated of a nitrocellulose base and containing 15-25 percent by weight of the polymerization reaction product of an aromatic vinyl compound with not less than about an equal molecular proportion of phenol as a plasticizer.

7. A stencil sheet comprising a porous base tissue formed of fibers highly oriented in the machine direction in which the dry tensile strength in the longitudinal direction is a minimum of 2500 grams for a two inch width while the dry tensile strength in the transverse direction is from 10-40 percent of said longitudinal tensile strength and a basis weight of 6.5 to 8.5 pounds calculated as the weight of 480 sheets of 24 by 36 inches, and a stencilizable coating on the base tissue based upon nitrocellulose and containing the polymerization reaction product of an aromatic vinyl compound with not less than about an equal molecular proportion of phenol as a plasticizer present in amounts ranging from 15-25 percent by weight.

8. A stencil sheet comprising a porous base tissue formed of fibers highly oriented in the machine direction in which the dry tensile strength in the longitudinal direction is between 2500-5500 grams for a two inch width while the dry tensile strength in the transverse direction is from 10-40 percent of said longitudinal tensile strength and a wet strength of at least 200 grams for a two inch width in the machine direction, and a stencilizable coating on the base tissue based upon nitrocellulose and containing the polymerization reaction product of an aromatic vinyl compound with not less than an equal molecular proportion of phenol as a plasticizer present in amounts ranging from 15-25 percent by weight.

References Cited in the file of this patent 

1. A PROCESS FOR PREPARING STENCIL SHEETS WHICH COMPRISES DEPOSITING A COATING COMPOSITION CONTAINING CELLULOSE NITRATE AS THE PRINCIPAL FILM FORMER AND 15 TO 25 PERCENT OF A POLYMERIZABLE REACTION PRODUCT OF AN AROMATIC VINYL COMPOUND WITH NOT LESS THAN AN EQUIMOLECULAR EQUIVALENT OF PHENOL AS A PLASTICIZER ON A POROUS BASE TISSUE IN WHICH THE DRY TENSIL STRENGTH IN THE LONGITUDINAL DIRECTION IS BETWEEN 2500-500 GRAMS FOR A TWO INCH WIDTH WHILE THE DRY TENSIL STRENGTH IN THE TRANSVERSE DIRECTION IS FROM 10-40 PERCENT OF SAID LONGITUDINAL TENSILE STRENGTH, A MINIMUM WET STRENGTH IN THE MACHINE DIRECTION OF ABOUT 200 GRAMS, BOTH WER AND DRY TENSILE STRENGTHS BEING FOR A TWO INCH WIDTH, AND A BASIS WEIGHT OF ABOUT 6.5 TO ABOUT 8.5 POUNDS FOR 480 SHEETS 24 BY 36 INCHES IN JIMENSION. 